using System;
using ANX.Framework.NonXNA.Development;

// This file is part of the ANX.Framework created by the
// "ANX.Framework developer group" and released under the Ms-PL license.
// For details see: http://anxframework.codeplex.com/license

namespace ANX.Framework
{
    [PercentageComplete(100)]
    [Developer("floAr")]
    [TestState(TestStateAttribute.TestState.InProgress)]
    public struct Ray : IEquatable<Ray>
    {
        #region fields
        /// <summary>
        /// The direction this ray is pointing to.
        /// </summary>
        public Vector3 Direction;

        /// <summary>
        /// Starting position of the ray.
        /// </summary>
        public Vector3 Position;
        #endregion

        #region constructors
        /// <summary>
        /// Initializes a new instance of the <see cref="Ray"/> struct.
        /// </summary>
        /// <param name="position">The position.</param>
        /// <param name="direction">The direction.</param>
        public Ray(Vector3 position, Vector3 direction)
        {
            this.Direction = direction;
            this.Position = position;
        }
        #endregion

        #region public methods
        /// <summary>
        /// Returns a hash code for this instance.
        /// </summary>
        /// <returns>
        /// A hash code for this instance, suitable for use in hashing algorithms and data structures like a hash table. 
        /// </returns>
        public override int GetHashCode()
        {
            return Position.GetHashCode() + Direction.GetHashCode();

        }
        /*
         *  Source for implementation :
         *  http://www-gs.informatik.tu-cottbus.de/projektstudium2006/doku/Strahlen_in_der_CG.pdf
         */
        /// <summary>
        /// Test if this <see cref="Ray"/> intersects with the specified <see cref="BoundingBox"/>.
        /// </summary>
        /// <param name="box">The box.</param>
        /// <returns>Distance from <see cref="Ray"/> start to interesection points</returns>
        public Nullable<float> Intersects(BoundingBox box)
        {
            Nullable<float> result;
            this.Intersects(ref box, out result);
            return result;
        }
        /// <summary>
        /// Test if this <see cref="Ray"/> intersects with the specified <see cref="BoundingBox"/>.
        /// </summary>
        /// <param name="box">The box.</param>
        /// <param name="result">The result.</param>
        public void Intersects(ref BoundingBox box, out Nullable<float> result)
        {
					box.Intersects(ref this, out result);
        }
        /// <summary>
        /// Test if this <see cref="Ray"/> intersects with the specified <see cref="BoundingFrustum"/>.
        /// </summary>
        /// <param name="frustum">The box.</param>
        /// <returns>Distance from <see cref="Ray"/> start to interesection points</returns>
        public Nullable<float> Intersects(BoundingFrustum frustum)
        {
					if (frustum == null)
					{
						throw new ArgumentNullException("frustum");
					}
					return frustum.Intersects(this); 
        }
        /// <summary>
        /// Test if this <see cref="Ray"/> intersects with the specified <see cref="BoundingSphere"/>.
        /// </summary>
        /// <param name="sphere">The sphere.</param>
        /// <returns>
        /// Distance from <see cref="Ray"/> start to interesection points
        /// </returns>
        public Nullable<float> Intersects(BoundingSphere sphere)
        {
            Nullable<float> result;
            this.Intersects(ref sphere, out result);
            return result;
        }
        /// <summary>
        /// Test if this <see cref="Ray"/> intersects with the specified <see cref="BoundingSphere"/>.
        /// </summary>
        /// <param name="sphere">The sphere.</param>
        /// <param name="result">The result.</param>
        public void Intersects(ref BoundingSphere sphere, out Nullable<float> result)
        {
            Vector3 toSphere = Vector3.Subtract(sphere.Center, this.Position);
            float lengthSquaredToSphere = toSphere.LengthSquared();
            float sphereRadiusSquared = sphere.Radius * sphere.Radius;

            //project the distance to the Sphere onto the Ray
            float toSphereOnRay = Vector3.Dot(this.Direction, toSphere);

            //ray starts in sphere
            if (lengthSquaredToSphere <= sphereRadiusSquared)
            {
                result = 0;
                return;
            }
            //if toSphere and this.Direction pointing in different directions
            if (toSphereOnRay < 0)
            {
                result = null;
                return;
            }

            float dist = sphereRadiusSquared + toSphereOnRay * toSphereOnRay - lengthSquaredToSphere;

            result = (dist < 0) ? null : toSphereOnRay - (float?)Math.Sqrt(dist);
        }

        /// <summary>
        /// Test if this <see cref="Ray"/> intersects with the specified <see cref="Plane"/>.
        /// </summary>
        /// <param name="plane">The plane.</param>
        /// <returns>
        /// Distance from <see cref="Ray"/> start to interesection points
        /// </returns>
        public Nullable<float> Intersects(Plane plane)
        {
            Nullable<float> result;
            this.Intersects(ref plane, out result);
            return result;
        }
        /// <summary>
        /// Test if this <see cref="Ray"/> intersects with the specified <see cref="Plane"/>.
        /// </summary>
        /// <param name="plane">The plane.</param>
        /// <param name="result">The result.</param>
        public void Intersects(ref Plane plane, out Nullable<float> result)
        {
            //http://www.cs.toronto.edu/~smalik/418/tutorial8_ray_primitive_intersections.pdf

            float vd = Vector3.Dot(plane.Normal, this.Direction);
          //As plane and Ray are infinitiv it intersects in every case, except the ray is parrales to the plane
            //no intersection if ray direction and plane normal are orthogional to each other
            if (vd == 0)
            {
                result = null;
                return;
            }
            float v0 = -Vector3.Dot(plane.Normal, this.Position) + plane.D;
            float t = v0 / vd;
            result=(this.Direction*t).Length();
        }

        /// <summary>
        /// Returns a <see cref="System.String"/> that represents this instance.
        /// </summary>
        /// <returns>
        /// A <see cref="System.String"/> that represents this instance.
        /// </returns>
        public override string ToString()
        {
            // This may look a bit more ugly, but String.Format should
            // be avoided cause of it's bad performance!
            return "{Position:" + Position.ToString() +
                " Direction:" + Direction.ToString() + "}";
        }
        #endregion

        #region operator overloading
        /// <summary>
        /// Implements the operator ==.
        /// </summary>
        /// <param name="a">First value</param>
        /// <param name="b">Second value</param>
        /// <returns>
        /// The result of the operator.
        /// </returns>
        public static bool operator ==(Ray a, Ray b)
        {
            return a.Direction == b.Direction && a.Position == b.Position;
        }
        /// <summary>
        /// Implements the operator !=.
        /// </summary>
        /// <param name="a">First value</param>
        /// <param name="b">Second value</param>
        /// <returns>
        /// The result of the operator.
        /// </returns>
        public static bool operator !=(Ray a, Ray b)
        {
            return a.Direction != b.Direction || a.Position != b.Position;
        }
        #endregion

        #region IEquatable implementation
        /// <summary>
        /// Determines whether the specified <see cref="System.Object"/> is equal to this instance.
        /// </summary>
        /// <param name="obj">The <see cref="System.Object"/> to compare with this instance.</param>
        /// <returns>
        ///   <c>true</c> if the specified <see cref="System.Object"/> is equal to this instance; otherwise, <c>false</c>.
        /// </returns>
        public override bool Equals(Object obj)
        {
            if (obj is Ray)
            {
                return this.Equals((Ray)obj);
            }
            return false;
        }

        /// <summary>
        /// Determines whether the specified <see cref="Ray"/> is equal to this instance.
        /// </summary>
        /// <param name="obj">The <see cref="Ray"/> to compare with this instance.</param>
        /// <returns>
        ///   <c>true</c> if the specified <see cref="Ray"/> is equal to this instance; otherwise, <c>false</c>.
        /// </returns>
        public bool Equals(Ray other)
        {
            return this.Direction == other.Direction && this.Position == other.Position;
        }
        #endregion
    }
}
